In a cement manufacturing process, it is well known to combine a calcareous material such as limestone/dolomite (CaCO3/CaMg(CO3)2 which is calcined with an argillaceous material such as shale/clay, silica, alumina, iron oxide, and similar materials. When heated to a temperature of approximately 1400° C., chemical reactions occur to convert the ingredients to calcium silicates, i.e., cement clinker. The clinker is subsequently milled to cement.
One typical commercial process for conventional cement manufacturing involves calcining and clinkering of cement raw materials by passing a mixture of finely divided raw material through a rotating inclined rotary vessel such as a conventional long wet or dry rotary kiln. In this process, the requisite temperatures are achieved by burning fuel such as gas, fuel oil, powdered coal, coke, and the like, singularly or in combinations in the gaseous atmosphere of the kiln with the gases moving counter current to the solids through the kiln. Given the high temperatures required for the process, fuel costs constitute a significant factor in the ultimate cost of the product. One of the more significant factors in a raw fuel costs for the production of cement clinker is the highly endothermic calcining step of converting calcium and magnesium carbonate to calcium and magnesium oxide (CaO and MgO) with the co-generation of carbon dioxide (CO2). By some calculations, this step alone accounts for more than 70% of the energy requirement of a typical dry clinkering process.
Other approaches in the art to address carbon dioxide emission from a cement production facility have included separation steps of isolating carbon dioxide produced by combustion and calcination as set forth in the WIPO publication WO 2008/059378 A2 entitled, “Process For The Production Of Cement”, and which is incorporated herein by reference.
While the art recognizes that CO2 production and capture from a cement manufacturing process are problems that need to be addressed, there remains room for improvement and variation within the art.